1. Field of the Invention
The present invention relates to a base tube for an electrophotographic photoconductive member, an electrophotographic photoconductive member using the same, and a method for producing the same. In particular, it relates to a base tube for an electrophotographic photoconductive member that is resistant to liquid retention to prevent bottom-end foaming from occurring due to the liquid retention in forming of a photoconductive layer, an electrophotographic photoconductive member using the same, and a method for producing the same.
2. Description of the Related Art
Generally, cylindrical base tubes, for example, of a metal, have been used as a base part for an electrophotographic photoconductive member. An electrophotographic photoconductive member is produced by forming a photoconductive layer containing a binder resin, a charge generating agent, a charge carrying agent, and others on the peripheral surface of such a base tube.
The method for forming a photoconductive layer usually includes the following steps:    (1) a coating step of coating a photoconductive-layer-coating solution on the peripheral surface of the base tube by immersing a base tube into a photoconductive-layer-coating solution prepared by dissolving a binder resin, a charge generating agent, a charge carrying agent, and others in an organic solvent,    (2) a drying step of drying the coated photoconductive-layer-coating solution, and    (3) a bottom end processing step of removing the part of the photoconductive layer on the bottom end by immersing the bottom end of the base tube previously inserted in the photoconductive-layer-coating solution into a solvent dissolving the photoconductive layer.
The bottom end processing step is carried out to ensure communication between the end of the base tube and a flange having a ground piece.
However, in the coating step, there has been observed a phenomenon of the photoconductive-layer-coating solution remaining at the bottom end of the base tube by the surface tension of the photoconductive-layer-coating solution when the base tube is lifted up from the photoconductive-layer-coating solution, (hereinafter, referred to as “liquid retention”). The liquid retention, in turn, lead to hindrance of flow of the photoconductive-layer-coating solution, causing a problem that air bubbles are contained in the photoconductive-layer-coating solution being solidified in the region close to the bottom of the base tube without being discharged downward (hereinafter, referred to as “bottom-end foaming”).
To solve the problems above, a base tube for an electrophotographic photoconductive member is formed with an end portion so modified in shape as to be resistant to liquid retention is proposed, for example, in Japanese Unexamined Patent Publication Nos. 2003-149842(D1) and 2003-149843(D2).
More specifically, literature D1 discloses a base tube 200 for an electrophotographic photoconductive member, having tapered projections 201 and tapered dents 202 formed continuously on the end face at one end portion 200′ of the cylindrical base tube 200 in an axial direction, as shown in FIG. 11A.
Alternatively, literature D2 discloses a base tube 210 for an electrophotographic photoconductive member, having slits 211 formed in an end portion 210′ of the cylindrical base tube 210 in the axial direction, as shown in FIG. 11B.
However, the base tubes for an electrophotographic photoconductive member described in literatures D1 and D2 could prevent liquid retention to some extent by improving the efficiency of dropwise discharge of the photoconductive-layer-coating solution, but the efficiency is still insufficient.
In addition, the shape of the end portion of the base tube is so complicated that great amounts of labor and cost are needed for forming into such a particular shape, and thus, the methods had a problem of economical disadvantage.
After intensive studies to solve the problems above, the inventors have found that it is possible to prevent liquid retention at a base tube end portion and bottom-end foaming caused by the liquid retention effectively, by forming a particular slanting portion on part of the cylindrical base tube, and completed the present invention.